Chorangioma

Chorioangioma is a vascular malformation, one of the most common tumors of the placenta. It is composed of tissue normally present in the placenta and does not metastasize. The large tumors are uncommon, occurring in 1:3,500 to 20,000 births. The chorioangioma can complicate the pregnancy with polyhydramnios, premature labor, hydrops, IUGR and fetal demise.
They usually are seen as circumscribed solid masses or complex masses that often protrude from the fetal surface of the placenta. Most reported tumors have been located near the umbilical cord insertion site; intraplacental tumors are more difficult to recognize. Polyhydramnios is present in one third of the cases.

Ultrasound image at 19 weeks showing complex mass.

Left image: Coronal T2 shows hyperintense mass in the placenta (black arrow). Note the small fetus (red arrow) and the presence of severe oligohydramnios. Right image: Sagittal T2 shows the tumor (red arrow).

Axial T2 showing the tumor (red arrow) and the fetus head (black arrow).